Steel alloy containing low chromium and copper

ABSTRACT

A LOW CARBON STEEL ALLOY OF HIGH TENSILE STRENGTH. THE STEEL ALLOY CONTAINS LESS THAN 0.23% CARBON, LESS THAN 0.5% SILICON, FROM 1,100 TO 1.50% MANGANESE, LESS THAN 0.040% PHOSPHORUS, LESS THAN 0.40% SULFUR, LESS THAN 0.30% COPPER, LESS THAN 0.50% CHROMIUM, FROM 0.010 TO 0.80% ALUMINUM, AND THE REMAINDER OF IRON AND IMPURTIES IN AN AMOUNT AND VARIETY WHICH DO NOT IMPAIR THE DESIRED CHARACTERISTICS OF THE ALLOY. THERE IS PREFERABLY NOT LESS THAN 0.20% SILICON AND FROM 1,00 TO 1.35% MANGANESE. THIS STEEL AFTER BEING ROLLED INTO A STEEL PLATE IS WELDED INTO A STEEL TUBE OF HIGH TENSILE STRENGTH. ALSO, THE STEEL ALLOY IS A KILLED STEEL AND IN PARTICULAR AN ALUMINUM KILLED STEEL.

United States Patent 3,554,734 STEEL ALLOY CONTAINING LOW CHROMIUM AND COPPER Osamu Kikkawa and Akira Kambayashi, Yokohama-shi, Japan, assignors to Nippon Kokan Kabushiki Kaisha, Tokyo, Japan No Drawing. Filed May 16, 1967, Ser. No. 638,720 Claims priority, applicatign 9Jilpau, Sept. 10, 1966,

Int. Cl. C22c 57/10, 39/02 US. Cl. 75124 4 Claims ABSTRACT OF THE DISCLQSURE less than 0.20% silicon and from 1.00 to 1.35% manganese. This steel after being rolled into a steel plate is welded into a steel tube of high tensile strength. Also, the steel alloy is a killed steel and in particular an aluminum killed steel.

BACKGROUND OF THE INVENTION The present invention relates to a low carbon steel alloy of high tensile strength.

'While this allo has many possible uses, it is particularly useful for the manufacture of welded steel tubes.

In particular, the present invention relates to a steel alloy of X-60 high tensile strength.

At the present time there are known steel alloys of X 60 high tensile strength used in the manufacture of steel tubes, but these alloys require as part of their composition columbium or vanadium, or both, in addition to manganese. According to the provisions of API (1966), it is specified that such alloys should contain less than 0.26% carbon, less than 1.35% manganese, less than 0.04% phosphorus, less than 0.050% sulfur, more than 0.01% Cb and more than 0.02% V. In addition it is specified that either one or both of Cb and V should be included in the alloy.

Inasmuch as steel alloys of this type are manufactured primarily according to the semi-killed method, these alloys do not have the fine grain structure of an alloy of high carbon content, and as a result they are required to be rolled under special low-temperature rolling conditions. As a result the eflicien'cy with which the rolling operations are carried out with conventional alloys of this type are considerably below an ideal rolling efiiciency. Furthermore, because of the carbon content, which is relatively high, the capability of welding the alloy in the field is poor. Also, because the alloy is a semi-killed steel, its strength is not uniformly distributed.

SUMMARY OF THE INVENTION It is accordingly a primary object of the present invention to provide a steel alloy of the above general type which will, however, avoid the above drawbacks. of the conventional steel alloys of this type.

In particular, it is an object of the invention to provide a low carbon steel alloy of high tensile strength which does not require the relatively expensive columbium and/or vanadium.

Furthermore, it is an object of the invention to provide a steel alloy which, while replacing the expensive columbium and/or vanadium with less expensive sub- Patented Jan. 12, 1971 stances, at the same time greatly increases the desirable characteristics of the alloy.

In addition, it is an object of the present invention to provide a steel alloy, which while highly suitable for many different uses, is particularly suitable for the manufacture of welded steel tubing.

Thus, it is an object of the invention to provide steel articles of high tensile strength and very high quality made of steel plates obtained by rolling a low carbon steel alloy of the above general type.

In accordance with the invention, the low carbon steel alloy of high tensile strength contains manganese, copper, and chromium, the relatively inexpensive copper and chromium being used to replace the far more expensive columbium and vanadium, while at the same time achieving' superior results. This alloy of the invention is rolled into steel plate which is then welded into steel tubing by a suitable welding method such as the UOE submerged arc welding method. In this way it is possible to provide steel tubes of X-60 hightensile strength, having in fact a tensile strength of more than 78,000 psi. The chemical composition of this low carbon steel alloy of the invention includes less than 0.23% carbon, less than 0.50% silicon, from 1.00 to 1.50% manganese, less than 0.040% phosphorus, less than 0.040% sulfur, less than 0.30% copper, less than 0.50% chromium, from 0.010 to 0.080% aluminum, and the remainder of iron and impurities the quantity and variety of which do not impair the desirable characteristics of the alloy.

In this way the strength of the low carbon steel alloy of the present invention having the above chemical composition is increased to the desired extent while utilizing inexpensive copper and chromium rather than the far more expensive columbium and vanadium. In addition, the cutting toughness of the alloy is improved and the desired characteristics thereof are stabilized by manufacturing the alloy according to the aluminum killed method.

As compared with conventional alloys of the above type containing columbium and vanadium, the carbon content of the alloy of the invention is substantially reduced so as to improve greatly its weldability. In addition, there is achieved with the alloy of the invention a fine grain structure which makes it possible to avoid the reduction in efliciency of the rolling operations necessarily inherent in the conventional alloys as a result of the temperature controls required due to the critical quantities of the various elements in the conventional alloys.

While the carbon content of the alloy of the invention is less than 0.23%, the minimum quantity of carbon is 0.10% in view of the value of carbon equivalent.

Inasmuch as silicon is included to provide the required strength for the material, the maximum quantity thereof should be 0.50% While the minimum quantity should be 0.20%. Otherwise the required strength is not achieved.

As is the case with conventional steel alloys, it is preferred that the quantities of sulfur and phosphorous should be quite low, but it was found that no deleterious effects were noted where the quantities for both of these elements did not exceed 0.040%.

Inasmuch as copper if present in an amount greater than 0.30% causes reheat brittleness during the rolling operations while chromium in a presence of more than 0.50% will in general result in an increase in the hardness of the material in view of the value of carbon equivalent, resulting in difliculties in connection with welding operations, the composition of the invention contains less than 0.30% copper and less than 0.50% chromium.

Because the granulation resulting from the presence of aluminum is not noticeable up to 0.10%, whereas cracks in the steel ingot will result where the aluminum is present in a quantity of more than 0.080%, the aluminum in the alloy of the invention is maintained between 0.010% and 0.080%.

Manganese in an amount of less than 1.00% does not provide the required strength while manganese in an amount of more than 1.50% impairs the Weldability of the alloy, in much the same way that chromium impairs the Weldability thereof if present in too great an amount. The manganese is maintained between 1.00 and 1.50%, preferably from 1.00 to 1.35%.

DESCRIPTION OF A PREFERRED EMBODIMENT The manner in which the present invention brings about the desired objects will be understood more fully from a consideration of the following preferred embodiment of the invention.

In accordance with the invention a steel tube of high tensile strength was manufactured by the above-discussed methods, namely by manufacturing the steel according to the aluminum killed process and then rolling the steel into the form of steel plate. The low carbon steel alloy of the invention contained 0.150.20% carbon, 0.20- 0.50% silicon, 1.00-1.35% manganese, 0.l0.20% copper, and 0.100.40% chromium.

The strength, cutting toughness, Weldability, inequality of strength distribution, anti-corrosive property and similar properties of a tube manufactured according to the submerged arc method from this alloy were compared with the corresponding properties of tubes made from conventional steel alloys, one of these alloys containing 0.160.26% carbon, 1.00-1.40% manganese, and 0.005- 0.04% columbium, while the other of the alloys with which the structure of the invention was compared contained 0.190.26% carbon, 1.00-1.30% manganese, and 0.01-0.09% vanadium, and both of these latter conventional steel alloys did not contain any silicon.

The results of the comparison were as follows:

(1) Preservation of strength With respect to preservation of strength (durability), the tube manufactured with the alloy of the invention and those manufactured with the conventional alloys showed in general the same tensile strength of more than 60,000 .s.i.

(2) Cutting toughness The tubes manufactured with the conventional alloys had 50% shear rupture temperature (50% fracture surface transition temperature) of -30 to +40 F., while the alloy steel of the present invention showed an improved 50% shear rupture temperature of 80 to -60 F.

(3) Weldability The steel alloy of the present invention had a weldability comparable in terms of carbon equivalent (USA) to alloys containing 0.330.49% columbium or 0.35- 0.45% vanadium. Thus, without using these latter expensive materials the alloy of the invention achieved weldability which could only be achieved with alloys having relatively large amounts of these expensive materials.

(4) Rolling efliciency Because of the temperature controls required by the conventional alloys there is a decrease in the rolling efficiency with the conventional alloys on the order of 15%, whereas there is absolutely no decrease in the rolling efiiciency when rolling the alloy of the present invention.

(5) Inequality of strength distribution With the conventional steel alloys manufactured according to the semi-killed process, the inequality of strength distribution was found to be 6-7 kg/mmP, while with the steel alloy of the present invention prepared according to the killed process the inequality of strength distribution was reduced to 4-5 kg./mm.

(6) Anti-corrosive property A comparison of the alloy of the invention with the conventional alloys showed a marked improvement in the anti-corrosive property. In particular, the extent of corrosion of the steel alloy of the invention was less than 10%, and this latter amount represented a marked improvement over the anti-corrosive properties of the conventional alloys.

It is apparent, therefore, that with the present invention it is possible to achieve a low carbon steel alloy of high tensile strength particularly suitable for the manufacture of steel tubes, although equally suitable for the manufacture of other articles, by making use of low carbon steels which have as part of their composition copper and chromium instead of making use of high carbon steels which have as part of their composition expensive columbium or vanadium. Using the low carbon steel of the alloy of the invention greatly improves the Weldability as compared to the conventional alloys. In addition, the granulation is brought about by way of the aluminum-killed method used in manufacturing the alloy of the invention instead of during the rolling operations, as has been conventional, so that not only is the efiiciency of the rolling operations improved but in addition the degree to which the inequality of the strength is distributed is decreased. It is therefore possible with the alloy of the invention to achieve articles such as steel tubes having high tensile strength and very high quality while utilizing an alloy and methods which are simple and inexpensive as compared to conventional alloys and methods.

While the above-described embodiment relates primarily to the production of API X-60 high tensile strength steel tubes, it is to be understood that the alloy of the invention may also be used in the manufacture of steel plates of high yield point, steel die blocks of various configurations, as well as other steel articles and in particular steel to be used at low temperatures.

What is claimed is:

1. A steel alloy of high tensile strength for welded steel tubes consisting essentially of between about 0.10% and less than 0.23% carbon, between about 0.20% and less than 0.50% silicon, from 1.00 to 1.35% manganese, less than 0.040% phosphorus, less than 0.040% sulfur, between about 0.10% and less than 0.30% copper, between about 0.10% and less than 0.50% chromium, from 0.010 to 0.080% aluminum, and the remainder substantially of iron.

2. An alloy according to claim 1, wherein the steel alloy is a killed steel.

3. An alloy according to claim 2, wherein said alloy is an aluminum killed steel.

4. A steel alloy according to claim 1 and wherein the amounts of carbon, silicon, manganese, copper and chromium are 0.150.20% carbon, 0.200.50% silicon, 1.01.35% manganese, 0.10-0.20% copper, and 0.10- 0.40% chromium.

References Cited UNITED STATES PATENTS 2,621,278 12/1952 Muller l24 1,931,717 10/1933 Buchholtz 75l24X 2,229,140 l/l941 Smith 75l24 3,207,637 9/1965 Matuschka 75l24X HYLAND BIZOT, Primary Examiner US. Cl. X.R. 75-125, 126 

